(1) Field of the Invention
The present invention relates to a main bearing for a crankshaft of an internal combustion engine, and more particularly relates to a main bearing for supporting a journal section of a crankshaft in a cylinder block lower portion of an internal combustion engine. Further, the present invention also relates to a bearing apparatus constituted by such a main bearing and a corresponding shaft section.
(2) Description of Related Art
A crankshaft of an internal combustion engine is supported at a journal section thereof in a cylinder block lower portion of the internal combustion engine via a main bearing formed of a pair of semi-cylindrical bearings. In order to lubricate the main bearing, lubricating oil which is discharged by an oil pump is fed into a lubricating oil groove which is formed along an inner circumferential surface of the main bearing, through an oil gallery which is formed in a wall of the cylinder block and a through port which is formed in a wall of the main bearing. In the crankshaft, a first lubricating oil path is formed by being penetrated in a diameter direction through the journal section, and communicates with the lubricating oil groove of the main bearing at both end openings of the first lubricating oil path. Furthermore, a second lubricating oil path is formed to branch from the first lubricating oil path and pass a crank arm section, and communicates with a third lubricating oil path which is formed by being penetrated in a diameter direction of a crankpin. Accordingly, the lubricating oil which is fed into the lubricating oil groove of the main bearing passes through the first lubricating oil path, the second lubricating oil path and the third lubricating oil path, and thereafter, is supplied to a slide surface between the crankpin and a connecting rod bearing from an end portion opening (lubricating oil outlet which is formed on an outer circumferential surface of the crankpin) of the third lubricating oil path.
The lubricating oil groove of the main bearing is formed on at least one of inner circumferential surfaces of a pair of semi-cylindrical bearings throughout an entire length in a circumferential direction thereof (FIG. 1 of Japanese Utility Model Publication No. 61-00573). In this case, the lubricating oil which is supplied to the lubricating oil groove of the main bearing from the oil gallery in the cylinder block mainly flows to the end portion in the circumferential direction of the semi-cylindrical bearing with rotation of the journal section, and most of the lubricating oil is discharged to an outside of the bearing through the axial direction groove formed in the joint portion of the pair of semi-cylindrical bearings.
Furthermore, in recent years, in response to miniaturization of the lubricating oil supplying oil pump with the objective of enhancing fuel efficiency of an internal combustion engine, there is also used a main bearing in which the length in the circumferential direction of the lubricating oil groove is configured to be shorter than the entire length in the circumferential direction of the semi-cylindrical bearing, and therefore, at least one of both end portions in the circumferential direction of the lubricating oil groove does not extend to the end portion in the circumferential direction of the semi-cylindrical bearing (namely, does not open at the axial direction groove), in order to reduce the leakage amount of the lubricating oil from the end portion in the circumferential direction of the semi-cylindrical bearing (see JP-Y2-61-000573, JP-A-04-219521, JP-A-2005-249024, JP-A-2011-179572 and JP-A-2008-095858).